* [PATCH v4 1/2] kho: fix deferred init of kho scratch
2026-02-20 16:52 [PATCH v4 0/2] kho: add support for deferred struct page init Michal Clapinski
@ 2026-02-20 16:52 ` Michal Clapinski
2026-02-20 16:52 ` [PATCH v4 2/2] kho: make preserved pages compatible with deferred struct page init Michal Clapinski
1 sibling, 0 replies; 3+ messages in thread
From: Michal Clapinski @ 2026-02-20 16:52 UTC (permalink / raw)
To: Evangelos Petrongonas, Pasha Tatashin, Mike Rapoport,
Pratyush Yadav, Alexander Graf, kexec, linux-mm
Cc: linux-kernel, Andrew Morton, Michal Clapinski
Currently, mm_core_init calls kho_memory_init, which calls
kho_release_scratch.
If DEFERRED is enabled, kho_release_scratch will first initialize the
struct pages of kho scratch. This is not needed. We can just let
page_alloc_init_late init it.
Next, kho_release_scratch will mark scratch as MIGRATE_CMA. If DEFERRED
is enabled, this will be overwritten later in deferred_free_pages.
To fix this, I removed the whole kho_release_scratch.
Marking the pageblocks as MIGRATE_CMA now happens in kho_init, which
runs after deferred_free_pages.
Signed-off-by: Michal Clapinski <mclapinski@google.com>
---
include/linux/memblock.h | 2 --
kernel/liveupdate/kexec_handover.c | 43 ++++++++----------------------
mm/memblock.c | 22 ---------------
3 files changed, 11 insertions(+), 56 deletions(-)
diff --git a/include/linux/memblock.h b/include/linux/memblock.h
index 221118b5a16e..35d9cf6bbf7a 100644
--- a/include/linux/memblock.h
+++ b/include/linux/memblock.h
@@ -614,11 +614,9 @@ static inline void memtest_report_meminfo(struct seq_file *m) { }
#ifdef CONFIG_MEMBLOCK_KHO_SCRATCH
void memblock_set_kho_scratch_only(void);
void memblock_clear_kho_scratch_only(void);
-void memmap_init_kho_scratch_pages(void);
#else
static inline void memblock_set_kho_scratch_only(void) { }
static inline void memblock_clear_kho_scratch_only(void) { }
-static inline void memmap_init_kho_scratch_pages(void) {}
#endif
#endif /* _LINUX_MEMBLOCK_H */
diff --git a/kernel/liveupdate/kexec_handover.c b/kernel/liveupdate/kexec_handover.c
index b851b09a8e99..de167bfa2c8d 100644
--- a/kernel/liveupdate/kexec_handover.c
+++ b/kernel/liveupdate/kexec_handover.c
@@ -1377,11 +1377,6 @@ static __init int kho_init(void)
if (err)
goto err_free_fdt;
- if (fdt) {
- kho_in_debugfs_init(&kho_in.dbg, fdt);
- return 0;
- }
-
for (int i = 0; i < kho_scratch_cnt; i++) {
unsigned long base_pfn = PHYS_PFN(kho_scratch[i].addr);
unsigned long count = kho_scratch[i].size >> PAGE_SHIFT;
@@ -1397,8 +1392,17 @@ static __init int kho_init(void)
*/
kmemleak_ignore_phys(kho_scratch[i].addr);
for (pfn = base_pfn; pfn < base_pfn + count;
- pfn += pageblock_nr_pages)
- init_cma_reserved_pageblock(pfn_to_page(pfn));
+ pfn += pageblock_nr_pages) {
+ if (fdt)
+ init_cma_pageblock(pfn_to_page(pfn));
+ else
+ init_cma_reserved_pageblock(pfn_to_page(pfn));
+ }
+ }
+
+ if (fdt) {
+ kho_in_debugfs_init(&kho_in.dbg, fdt);
+ return 0;
}
WARN_ON_ONCE(kho_debugfs_fdt_add(&kho_out.dbg, "fdt",
@@ -1421,35 +1425,10 @@ static __init int kho_init(void)
}
fs_initcall(kho_init);
-static void __init kho_release_scratch(void)
-{
- phys_addr_t start, end;
- u64 i;
-
- memmap_init_kho_scratch_pages();
-
- /*
- * Mark scratch mem as CMA before we return it. That way we
- * ensure that no kernel allocations happen on it. That means
- * we can reuse it as scratch memory again later.
- */
- __for_each_mem_range(i, &memblock.memory, NULL, NUMA_NO_NODE,
- MEMBLOCK_KHO_SCRATCH, &start, &end, NULL) {
- ulong start_pfn = pageblock_start_pfn(PFN_DOWN(start));
- ulong end_pfn = pageblock_align(PFN_UP(end));
- ulong pfn;
-
- for (pfn = start_pfn; pfn < end_pfn; pfn += pageblock_nr_pages)
- init_pageblock_migratetype(pfn_to_page(pfn),
- MIGRATE_CMA, false);
- }
-}
-
void __init kho_memory_init(void)
{
if (kho_in.mem_map_phys) {
kho_scratch = phys_to_virt(kho_in.scratch_phys);
- kho_release_scratch();
kho_mem_deserialize(phys_to_virt(kho_in.mem_map_phys));
} else {
kho_reserve_scratch();
diff --git a/mm/memblock.c b/mm/memblock.c
index 6cff515d82f4..3eff19124fc0 100644
--- a/mm/memblock.c
+++ b/mm/memblock.c
@@ -959,28 +959,6 @@ __init void memblock_clear_kho_scratch_only(void)
{
kho_scratch_only = false;
}
-
-__init void memmap_init_kho_scratch_pages(void)
-{
- phys_addr_t start, end;
- unsigned long pfn;
- int nid;
- u64 i;
-
- if (!IS_ENABLED(CONFIG_DEFERRED_STRUCT_PAGE_INIT))
- return;
-
- /*
- * Initialize struct pages for free scratch memory.
- * The struct pages for reserved scratch memory will be set up in
- * reserve_bootmem_region()
- */
- __for_each_mem_range(i, &memblock.memory, NULL, NUMA_NO_NODE,
- MEMBLOCK_KHO_SCRATCH, &start, &end, &nid) {
- for (pfn = PFN_UP(start); pfn < PFN_DOWN(end); pfn++)
- init_deferred_page(pfn, nid);
- }
-}
#endif
/**
--
2.53.0.345.g96ddfc5eaa-goog
^ permalink raw reply [flat|nested] 3+ messages in thread* [PATCH v4 2/2] kho: make preserved pages compatible with deferred struct page init
2026-02-20 16:52 [PATCH v4 0/2] kho: add support for deferred struct page init Michal Clapinski
2026-02-20 16:52 ` [PATCH v4 1/2] kho: fix deferred init of kho scratch Michal Clapinski
@ 2026-02-20 16:52 ` Michal Clapinski
1 sibling, 0 replies; 3+ messages in thread
From: Michal Clapinski @ 2026-02-20 16:52 UTC (permalink / raw)
To: Evangelos Petrongonas, Pasha Tatashin, Mike Rapoport,
Pratyush Yadav, Alexander Graf, kexec, linux-mm
Cc: linux-kernel, Andrew Morton, Michal Clapinski
From: Evangelos Petrongonas <epetron@amazon.de>
When CONFIG_DEFERRED_STRUCT_PAGE_INIT is enabled, struct page
initialization is deferred to parallel kthreads that run later
in the boot process.
During KHO restoration, deserialize_bitmap() writes metadata for
each preserved memory region. However, if the struct page has not been
initialized, this write targets uninitialized memory, potentially
leading to errors like:
BUG: unable to handle page fault for address: ...
Fix this by introducing kho_get_preserved_page(), which ensures
all struct pages in a preserved region are initialized by calling
init_deferred_page() which is a no-op when deferred init is disabled
or when the struct page is already initialized.
Signed-off-by: Evangelos Petrongonas <epetron@amazon.de>
Co-developed-by: Michal Clapinski <mclapinski@google.com>
Signed-off-by: Michal Clapinski <mclapinski@google.com>
Reviewed-by: Pratyush Yadav (Google) <pratyush@kernel.org>
Reviewed-by: Pasha Tatashin <pasha.tatashin@soleen.com>
Reviewed-by: Mike Rapoport (Microsoft) <rppt@kernel.org>
---
I think we can't initialize those struct pages in kho_restore_page.
I encountered this stack:
page_zone(start_page)
__pageblock_pfn_to_page
set_zone_contiguous
page_alloc_init_late
So, at the end of page_alloc_init_late struct pages are expected to be
already initialized. set_zone_contiguous() looks at the first and last
struct page of each pageblock in each populated zone to figure out if
the zone is contiguous. If a kho page lands on a pageblock boundary,
this will lead to access of an uninitialized struct page.
There is also page_ext_init that invokes pfn_to_nid, which calls
page_to_nid for each section-aligned page.
There might be other places that do something similar. Therefore, it's
a good idea to initialize all struct pages by the end of deferred
struct page init. That's why I'm resending Evangelos's patch.
I also tried to implement Pratyush's idea, i.e. iterate over zones,
then get node from zone. I didn't notice any performance difference
even with 8GB of kho.
---
kernel/liveupdate/Kconfig | 2 --
kernel/liveupdate/kexec_handover.c | 27 ++++++++++++++++++++++++++-
2 files changed, 26 insertions(+), 3 deletions(-)
diff --git a/kernel/liveupdate/Kconfig b/kernel/liveupdate/Kconfig
index 1a8513f16ef7..c13af38ba23a 100644
--- a/kernel/liveupdate/Kconfig
+++ b/kernel/liveupdate/Kconfig
@@ -1,12 +1,10 @@
# SPDX-License-Identifier: GPL-2.0-only
menu "Live Update and Kexec HandOver"
- depends on !DEFERRED_STRUCT_PAGE_INIT
config KEXEC_HANDOVER
bool "kexec handover"
depends on ARCH_SUPPORTS_KEXEC_HANDOVER && ARCH_SUPPORTS_KEXEC_FILE
- depends on !DEFERRED_STRUCT_PAGE_INIT
select MEMBLOCK_KHO_SCRATCH
select KEXEC_FILE
select LIBFDT
diff --git a/kernel/liveupdate/kexec_handover.c b/kernel/liveupdate/kexec_handover.c
index de167bfa2c8d..fe9c88fd2541 100644
--- a/kernel/liveupdate/kexec_handover.c
+++ b/kernel/liveupdate/kexec_handover.c
@@ -457,6 +457,31 @@ static int kho_mem_serialize(struct kho_out *kho_out)
return err;
}
+/*
+ * With CONFIG_DEFERRED_STRUCT_PAGE_INIT, struct pages in higher memory regions
+ * may not be initialized yet at the time KHO deserializes preserved memory.
+ * KHO uses the struct page to store metadata and a later initialization would
+ * overwrite it.
+ * Ensure all the struct pages in the preservation are
+ * initialized. deserialize_bitmap() marks the reservation as noinit to make
+ * sure they don't get re-initialized later.
+ */
+static struct page *__init kho_get_preserved_page(phys_addr_t phys,
+ unsigned int order)
+{
+ unsigned long pfn = PHYS_PFN(phys);
+ int nid;
+
+ if (!IS_ENABLED(CONFIG_DEFERRED_STRUCT_PAGE_INIT))
+ return pfn_to_page(pfn);
+
+ nid = early_pfn_to_nid(pfn);
+ for (unsigned long i = 0; i < (1UL << order); i++)
+ init_deferred_page(pfn + i, nid);
+
+ return pfn_to_page(pfn);
+}
+
static void __init deserialize_bitmap(unsigned int order,
struct khoser_mem_bitmap_ptr *elm)
{
@@ -467,7 +492,7 @@ static void __init deserialize_bitmap(unsigned int order,
int sz = 1 << (order + PAGE_SHIFT);
phys_addr_t phys =
elm->phys_start + (bit << (order + PAGE_SHIFT));
- struct page *page = phys_to_page(phys);
+ struct page *page = kho_get_preserved_page(phys, order);
union kho_page_info info;
memblock_reserve(phys, sz);
--
2.53.0.345.g96ddfc5eaa-goog
^ permalink raw reply [flat|nested] 3+ messages in thread